H number of thiosemicarbazones and their 1: 1 copper complexes are described and the possible structures of the latter are discussed. Formation of copper complexes from aromatic aldehyde and ketone thiosemicarbazo~~es results in a loss of one H atom as indicated by infrared spectra. In the aliphatic series, no loss of H atom is apparent upon complex formation.I t is reasonable to assume that diflerent processes are involved resulting in two possible structures for the aromatic and the aliphatic copper co~nplexes. Some chemical evidence supports this view.